I. Field of the Invention
The present invention relates generally to wireless telephone systems, and more particularly to voice mail systems for CDMA wireless telephone systems.
II. Description of the Related Art
Voice mail systems are ubiquitous in modern telephone systems, including wireless telephone systems. In the wireless telephone context, however, current voice mail systems can degrade recorded messages, because the recorded messages are encoded and decoded multiple times.
More particularly, in the context of code division multiple access (CDMA) wireless telephone systems, a transmitting telephone encodes voice signals using a vocoder, prior to transmitting the signals over the air. A preferred CDMA system is described in U.S. Pat. Nos. 4,901,307 and 5,103,459, both of which are assigned to the same assignee as is the present invention and both of which are incorporated herein by reference. Also, a preferred vocoder is disclosed in U.S. Pat. No. 5,414,796, which is also assigned to the same assignee as is the present invention and which is incorporated herein by reference.
When a person attempts to call a wireless station user from a landline telephone, the call is routed through a public switch telephone network (PSTN). The PSTN connects the call to a base station controller (BSC) which controls the operation of a plurality of base stations that serve a common geographic area. When it receives the call from the PSTN or another wireless telephone, the BSC determines whether the recipient wireless telephone is currently registered with any base station. If the wireless telephone is not registered (or it is registered but it does not pick up), the call is directed to a voice mail system that encodes and stores a voice message intended for the recipient wireless telephone user.
Subsequently, the wireless telephone user can access the voice mail system to retrieve the message, at which time the message is decoded and sent to the BSC. At the BSC, the message is once again encoded, then sent to a base station for transmission to the wireless telephone. Upon receipt of the message, the wireless telephone must once again decode the message. Hence, in existing wireless telephone system voice mail systems, a voice mail message undergoes two encoding/decoding cycles, once when the message is stored and again when the receiving person accesses his or her voice mail. Unfortunately, the quality of the voice message is degraded as an undesirable consequence of multiple encodings and decodings.
Accordingly, it is an object of the present invention to provide a voice mail system for a wireless telephone system which renders relatively high quality voice mail messages. Another object of the present invention is to provide a voice mail system for a wireless telephone system which minimizes the number of encoding/decoding cycles voice mail messages must undergo. Still another object of the present invention is to provide a voice mail system for a wireless telephone system which is easy to use and cost-effective to manufacture and implement.